1. Field of the Invention
The present invention relates to an image processing apparatus which detects a document region and a determination method.
2. Description of the Related Art
Image reading apparatuses designed to optically read documents and photographs and convert the read data into electronic data are widely known. Recently, in general, such apparatuses have been used as multifunctional apparatuses having multiple functions such as a printing function, data transmission/reception function, copying function, and facsimile function as well as being used in a single standalone form. The hardware resource environment including CPUs, memories, and liquid crystal screens, which execute these processes, has remarkably advanced and greatly improved in performance. It is regarded important to provide more comfortable use environments to users by making the most use of these hardware resources. For example, it is important to provide an environment that implements high-level image processing without requiring any complicated operation for even a user who has no advanced knowledge.
Such image processing includes, for example, document region detection processing of detecting a document region from a reading result. Japanese Patent Laid-Open No. 61-20936 discloses a technique of estimating a paper size such as A4 or B5 based on the detection results obtained by a plurality of sensors provided under a glass document table. In addition, Japanese Patent Laid-Open No. 2001-256491 discloses a technique of discriminating a background from a document region by holding the range of the colors of background portions in advance and determining whether a target portion is included in the range. Japanese Patent Laid-Open No. 2001-256491 further discloses a technique of estimating a size while performing edge detection.
As sheets of paper to be read by an image reading apparatus, so-called sheets of plain paper are often used. Plain paper ranges from recycled paper made by recycling used paper to high-quality paper and varies widely in paper color, whiteness degree, and thickness. Conventionally, many types of recycled paper are tinged with yellow as compared with high-quality paper. However, an increasing number of types of recycled paper have the same whiteness as that of high-quality paper. As a consequent, plain paper with a high whiteness degree has been generally used.
The technique disclosed in Japanese Patent Laid-Open No. 2001-256491 is designed to detect a document region based on the held color data of background colors. If, however, a background has a color close to that of a document region, it is very difficult to detect the document region. If, for example, a reading target is a photographic document, since photographic data is printed on almost the entire region of a surface of the document sheet, any problems hardly occur in detection of a document region.
If, however, a reading target is a text document mainly including characters, non-printed regions on a surface of the document sheet are predominantly larger in number than printed regions. In addition, a white sheet is often used on a surface of the document table cover of an image reading apparatus which comes into contact with the document table. Such a white sheet is used to eliminate the necessity to use any extra ink or toner when processing a region corresponding to a marginal portion other than a document region in processing that includes printing processing such as copying operation and facsimile operation.
That is, it is difficult to accurately detect a document region by using the technique disclosed in Japanese Patent Laid-Open No. 2001-256491 in consideration of (a) plain paper improved in the degree of whiteness with high use frequency, (b) reading of a text document mostly occupied by non-printed regions, and (c) a white sheet used on a surface of a document table cover which comes into contact with a document table. As a result, part of a document region may not be detected or one document may be detected upon being segmented into a plurality of regions.
The detection method using the sensors disclosed in Japanese Patent Laid-Open No. 61-20936 can detect a document region regardless of the type and color of a document. However, this method is designed to perform detection at fixed positions, and hence to detect only documents with standardized sizes as reading targets. When detecting a document region, the user needs to place a document at corners of the document table or at a predetermined abutment portion. In addition, according to the detection method using the sensors disclosed in Japanese Patent Laid-Open No. 61-20936, when the user places a plurality of documents with small sizes such as name cards, the sizes may be erroneously detected. Furthermore, the cost of the apparatus increases by the number of sensors mounted in the apparatus.